1. Field of the Invention
The present invention relates to a mechanical pencil, and more particularly to a mechanical pencil including an external cylinder, a lead delivery mechanism set in the external cylinder, and a lead holder set before the lead delivery mechanism in the external cylinder to gently hold a lead, in which the lead delivery mechanism has a lead-fastening chuck which fastens a lead and moves back and forth in the external cylinder, thereby to deliver the lead toward the front end of the external cylinder.
2. Description of the Related Art
In some conventional mechanical pencils, a lead-fastening chuck generally has a plurality of chuck elements and fastens a lead by holding the lead with the chuck elements under the normal state. A slider-type lead pipe is set to the front end of an external cylinder, depending on the type of mechanical pencil, to surround the circumference of a lead portion positioned to the front end of the external cylinder. When it is necessary to protrude the lead beyond the front end of the external cylinder in order to perform writing, or when it is necessary to further protrude the lead beyond the front end of the external cylinder because the lead is exhausted due to writing, it is possible to deliver the lead forwardly by operating a lead delivery mechanism.
More specifically, a lead-fastening chuck and a chuck ring for fastening the lead-fastening chuck advance by a predetermined distance together with the lead and moreover, only the lead-fastening chuck advances by being released from the chuck ring, and the chuck elements of the lead-fastening chuck release the lead. The lead holder set before the lead delivery mechanism holds the advanced lead, the lead-fastening chuck and chuck ring retreat to their initial positions, and the lead-fastening chuck firmly holds the lead again.
Thus, the lead is delivered by a predetermined distance. Moreover, for a mechanical pencil having a slider-type lead pipe, when a lead pipe remains in an external cylinder and a lead-fastening chuck advances, the lead-fastening chuck presses a lead holder and the lead pipe forwardly.
As described above, in a conventional mechanical pencil, a moving margin for a lead-fastening chuck to advance in order to deliver a lead is necessary between the lead-fastening chuck and a lead holder, and a spatial portion is formed in the moving margin. Because a broken lead can enter the spatial portion, the broken lead may enter the gap between the chuck elements of the lead-fastening chuck or may remain between the lead-fastening chuck and the lead holder, thereby preventing (or hindering) the lead-fastening chuck from advancing and rendering the chuck inoperable.
In view of the foregoing and other problems, drawbacks, and disadvantages of the conventional structures, an object of the present invention is to provide a mechanical pencil capable of protecting a lead present between a lead-fastening chuck and a lead holder, and preventing a broken lead from entering the gap between them.
To attain the above and other objects, in a first aspect of the present invention, a mechanical pencil includes an external cylinder, a lead delivery mechanism disposed in the external cylinder, and a lead holder disposed before the lead delivery mechanism in the external cylinder to gently hold a lead. Preferably, the lead delivery mechanism has a lead-fastening chuck which fastens a lead and moves back and forth in the external cylinder, to deliver the lead toward the front end of the external cylinder. A guide member preferably is arranged between the lead-fastening chuck and the lead holder in the external cylinder and is always urged backwardly toward the lead-fastening chuck to protect a lead portion between the lead-fastening chuck and a lead holding portion of the lead holder.
Because the lead portion formed before the lead-fastening chuck is protected by the guide member set between the lead-fastening chuck and the lead holder, a broken lead can be prevented from entering (and remaining) in a space between the lead-fastening chuck and the lead holder, thereby preventing a malfunction. Because the guide member is always urged backwardly toward the lead-fastening chuck, a gap always can be prevented from being formed in the axial direction between the guide member and the lead-fastening chuck and the lead portion ahead of the lead-fastening chuck can be fixedly protected.
Moreover, it is possible to always overlap the front end of the guide member and the rear end of the lead holder with each other in the axial direction by inserting either of the front end or the rear end into the other end. Because the front end of the guide member always overlaps with the rear end of the lead holder in the axial direction, it is possible to fixedly protect the lead portion formed between the lead-fastening chuck and the lead holder by always preventing a gap from being formed in the axial direction between the guide member and the lead holder.
Furthermore, the guide member can have a plurality of protective elements separated from each other in the circumferential direction to protect the outer periphery of a lead, and it is possible to insert the rear end of the lead holder between the adjacent protective elements.
Furthermore, the guide member can be formed by an annular flange and a plurality of insertion legs extending forward from the flange, and the rear end of the lead holder can be inserted between the adjacent insertion legs. Alternatively, the guide member can be formed by an annular flange and a cylindrical portion before the flange, with a plurality of ribs formed on the inner periphery of the cylindrical portion separately from each other in the circumferential direction, and the rear end of the lead holder can be inserted between the adjacent ribs.
Furthermore, the rear end of the lead holder can have a plurality of holding elements separated from each other in the circumferential direction to hold the outer periphery of a lead, and the front end of the guide member can be inserted between the adjacent holding elements.
Furthermore, the rear end of the lead holder can be formed into a cylindrical portion and a plurality of ribs can be formed on the inner periphery of the cylindrical portion separately from each other in the circumferential direction, and the front end of the guide member can be inserted between the adjacent ribs. Alternatively, the rear end of the lead holder can have a plurality of insertion legs extending backward, and the front end of the guide member can be inserted between the adjacent insertion legs.
Further, a protrusion may be formed elastically contacting the inner periphery of the external cylinder on the outer periphery of the lead holder. Thus, the lead holder can fixedly hold a lead so that the lead holder is not easily moved due to the friction with the inside of the external cylinder by, for example, the load received from the lead. By forming the protrusion integrally with the lead holder, the number of components and the assembly labor can be decreased.
Moreover, the lead holder may be formed so that it can be pushed forwardly by the guide member in the external cylinder, and it can be held at an advancing position during writing. Alternatively, the lead holder can be formed so that it does not move in the external cylinder under any operation.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2001-245537, filed on Aug. 13, 2001, which is expressly incorporated herein by reference in its entirety.